1. Field of The Invention
The present invention relates generally to an improvement on an analog indicator which may be employed in a tachometer, a speedometer, or so forth for an automotive vehicle. More particularly, the invention is directed to an analog indicator including a self-luminescent indicating pointer which is simple in design and has a high indicating accuracy.
2. Description of The Prior Art
Japanese Patent First Publication No. 4-204323, assigned to the same assignee as the present application, discloses a self-luminescent pointer device for a gauge which may be used with an automotive speedometer or a tachometer. This conventional pointer device includes a plurality of light emitting diodes (LEDs) arranged on an indicating pointer to improve visibility of pointer deflection over a dial plate.
In such a self-luminescent pointer device, lead wires for carrying lighting current to the LEDs on the indicating pointer need to be provided rotatably along with rotation of the indicating pointer. A pair of hairsprings are arranged vertically around the periphery of an indicating support shaft to be utilized as lead wires connecting with positive and negative terminals of the LEDs respectively. Additionally, an insulating plate is disposed between the upper and lower hairsprings for avoiding a short circuit therebetween. Therefore, in order to provide a space for arranging the upper and lower hairsprings around the pointer support shaft, it is necessary for the pointer support shaft to be lengthened, resulting in increasing the entire thickness of the indicator device. In addition, a load acting on a bearing of the pointer support shaft is increased, causing friction to develop between the bearing and the pointer support shaft with the result that the hysteresis of the indicating pointer is undesirably increased and thus degrade the indicating accuracy of the device.
Further, a typical thin hairspring is usually made of a phosphor bronze so as to have fine conductivity and spring elasticity. When using such a metal hairspring, a drawback may be encountered in that part of the hairspring vibrates due to rotation of the indicating pointer to cause adjacent surfaces of the hairspring to contact with each other, generating noise undesirably.